1. Field of the Invention
The present invention relates to a trigger switch used in electric tools.
2. Description of the Related Art
Conventionally, there is widely used a trigger switch disposed in a grip portion of the electric tool, which a user draws with a finger to start up the electric tool.
As disclosed in Japanese Patent Publication No. 1996-28146 and U.S. Pat. No. 6,104,105, there is well known a trigger switch in which a seesaw type contact pair is operated using a slide member slid by manipulation of a trigger. The seesaw type contact pair includes a movable piece, an arm portion, and a lever portion. A center portion of the movable piece is supported, and the movable piece is extended from a fulcrum toward a direction in which the trigger is drawn. A movable contact is located at a front end of the movable piece, and the movable contact touches on a fixed contact provided outside the movable piece. The arm portion is biased by a spring such that the movable contact touches on the fixed contact. The lever portion is extended on the opposite side to the arm portion, the lever portion touches on the slide member to be widened outward, and the lever portion inwardly rotates the arm portion against a biasing force of the spring.
Miniaturization of the trigger switch is needed to improve operability of the electric tool. When a helical spring draws the movable piece to bias the movable piece as shown in FIG. 1 of Japanese Patent Publication No. 1966-28146, the trigger switch cannot be miniaturized because the helical spring is extended off the outside of the fixed contact.
In the case where the movable piece is biased from the inside by a compression spring, it is necessary that a spring seat to which one end of the compression spring is fixed be formed outside a guide structure of the slide member or the spring biasing the trigger. When the trigger switch is miniaturized as shown in FIG. 2 of U.S. Pat. No. 6,104,105, it is necessary that the spring be shortened during compression in order to ensure a stroke of the contact. Therefore, unfortunately reliability is lowered because sufficient pressure-contact force cannot be obtained to the fixed contact.